Powdery Mildew Cycle
The first evidence of powdery mildew on a zucchini plant is whitish-gray powdery spots on the leaves, stems, or flowers. If the infection is not stopped, the spots spread creating a powdery whitish-gray mat resembling flour dust.
Prior to the whitish-gray spots appearing, spores are dispersed into the air by the wind. This begins happening when the daytime temperature rises above 60°F (16°C). When favorable environmental conditions are present, the spores come into contact with the zucchini plant and infection begins.
The fungus infection overwinters in the garden if infected plant debris is not removed. In the spring, the cycle is repeated.
Preventing Powdery Mildew
Powdery mildew spores begin infecting the zucchini plant when the environmental conditions are just right. Temperatures of 60°F to 80°F (16°C to 27°C), high humidity, and shady areas encourage rapid growth of this fungal infection. Temperatures over 90°F (32°C) plus direct sunlight discourage powdery mildew. Here are suggestions to prevent powdery mildew:
- Plant powdery mildew resistant zucchini varieties.
- Do not plant unhealthy plants.
- Plant in area that receives six or more hours of direct sunlight per day.
- Water zucchini plants in the morning so leaves have time to dry before night.
- Water at the base of the plant and not overhead.
- Disinfect garden tools with bleach.
- Remove leaves infected with powdery mildew and discard.
- Zucchini plants should be at least 3 feet apart.
- Do not excessively use fertilizer.
Sometimes even after following the above suggestions, zucchini plants can still become infected with powdery mildew; however, all hope for fruitful plants is not gone. This disease can be reduced or killed with natural products. Here are three remedies that may be effective:
Baking Soda Spray
If applied early in the powdery mildew outbreak, a mixture of 1 TBSP of baking soda, 1 tsp of dormant oil, 1 tsp of insecticidal soap (not detergent), and 1 gallon of water can be effective against powdery mildew. Spray the infected plants weekly.
Organic Milk Spray
A mixture of nine parts water and one part unpasteurized milk is an organic fungicide that may be effective against powdery mildew. Spray weekly the entire plant including the underside of the [link u=zucchini-leaves}leaves[/link}.
Potassium Bicarbonate Spray
Potassium bicarbonate has been scientifically proven to kill powdery mildew. Mix 3 TBSP of potassium bicarbonate, 3 TBSP of vegetable oil, 1/2 tsp of soap, and 1 gallon of water to make this effective fungicide.